Laminated balun transformer

ABSTRACT

A laminated balun transformer includes first line elements which are connected in series through a relay terminal, to constitute an unbalanced transmission line. Other line elements each constitute a balanced transmission lines. Strip lines are electromagnetically coupled to constitute a coupler. Similarly, other line elements are electromagnetically coupled to constitute a coupler. A ground terminal is connected to the balanced transmission lines, which are constituted by a pair of the line elements. Meanwhile, a shield terminal is connected to leading portions of shield electrodes. These two terminals are electrically independent of each other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to laminated balun transformers, and moreparticularly, to a laminated balun transformer for use as abalanced-to-unbalanced signal converter, a phase transformer, or othersuitable device for an IC for a radio communication apparatus.

2. Description of the Related Art

A balun transformer is used to convert, for example, a balanced signalfrom a balanced transmission line into an unbalanced signal for anunbalanced transmission line or to convert an unbalanced signal from anunbalanced transmission line into a balanced signal for a balancedtransmission line. The term “balun” is an abbreviation of“BALanced-UNbalanced”.

A balanced transmission line has a pair of signal lines, through which asignal (a balanced signal) propagates as a potential differencetherebetween. In a balanced transmission line, the two signal lines areequally affected by external noise, thereby canceling out the externalnoise. Thus, the balanced transmission line has an advantage in that itis less susceptible to the influence of external noise. In addition,since the internal circuit of an analog IC includes a differentialamplifier, the input/output terminals for a signal for the analog ICare, in many cases, of a balanced type that outputs or inputs a signalas a potential difference between the two terminals.

In contrast, in an unbalanced transmission line, a signal (unbalancedsignal) propagates as a potential of a single signal line relative to aground potential (zero potential). Examples of an unbalancedtransmission line include a coaxial line and a microstrip line disposedon a substrate.

Conventionally, a laminated balun transformer 1 shown in FIG. 7 has beenproposed as a balanced-to-unbalanced converter for a transmission linein a radio-frequency circuit.

The balun transformer 1 includes dielectric sheets 2 a to 2 h. On thesurface of the dielectric sheet 2 b, a lead electrode 3 is provided. Onthe dielectric sheets 2 c, 2 d, 2 f, and 2 g, ¼ wavelength strip lines4, 5, 8, and 9 are provided, respectively. On the surfaces of thedielectric sheets 2 a, 2 e, and 2 h, shield electrodes 12, 13, and 14are provided, respectively.

The strip lines 4 and 9 are electrically connected in series through arelay terminal N, which is provided on an outer surface, to constitutean unbalanced transmission line. The strip lines 5 and 8, on the otherhand, each constitute a balanced transmission line.

The strip line 5 is arranged so as to oppose the strip line 4 with thesheet 2 c being interposed therebetween. Thus, the strip lines 4 and 5are electromagnetically coupled to constitute a coupler. The strip line9 is arranged so as to oppose the strip line 8 with the sheet 2 finterposed therebetween. Thus, the strip lines 8 and 9 areelectromagnetically coupled to constitute a coupler. The strip lines 5and 9 are connected in series through a via hole 18 that is formed inthe sheets 2 d and 2 e.

Meanwhile, in some cases, a balun transformer 1 for use in an mobilecommunication apparatus, such as a portable telephone, or a wireless LANare required to amplify a balanced signal by applying a bias to only thebalanced transmission lines.

In the balun transformer 1 described above, however, one end of thestrip line 5 and one end of the strip line 8, which constitute thebalanced transmission lines, are electrically connected to a shieldterminal G via a shield electrode 13. Thus, it is impossible to apply abias voltage to only the balanced transmission lines. In other words,the balun transformer 1 having such a configuration has a problem inthat a balanced signal cannot be amplified.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodimentsof the present invention provide a laminated balun transformer thatallows a bias voltage to be applied to only transmission lines toamplify a balanced signal.

According to a preferred embodiment of the present invention, alaminated balun transformer includes a stack in which, at least, a pairof balanced transmission lines, an unbalanced transmission line that iselectromagnetically coupled with the pair of balanced transmissionlines, a shield electrode that opposes at least one of the balancedtransmission lines and the unbalanced transmission line, and a pluralityof dielectric layers are stacked, a ground terminal that is provided ona surface of the stack and that is electrically connected to thebalanced transmission lines, and a shield terminal that is provided on asurface of the stack and that is electrically connected to the shieldelectrode.

One of the unique features of the laminated balun transformer is thatthe ground terminal and the shield terminal are electrically independentof each other.

With this arrangement, since the ground terminal that is electricallyindependent of the shield terminal is provided, for example, a biasvoltage can be applied to only the ground terminal.

In addition, another preferred embodiment of the present inventionprovides a laminated balun transformer that includes a pair of balancedtransmission lines, an unbalanced transmission line that iselectromagnetically coupled with the pair of balanced transmissionlines, an unbalanced signal terminal that is electrically connected toone end of the unbalanced transmission line, two balanced signalterminals, each terminal being electrically connected to one end of onecorresponding balanced transmission line, a common bias terminal that iselectrically connected to the other ends of the balanced transmissionlines, and a bias capacitor that is electrically connected between thecommon bias terminal and ground.

In addition, another preferred embodiment provides a laminated baluntransformer that includes a stack in which, at least, a pair of balancedtransmission lines, an unbalanced transmission line that iselectromagnetically coupled with the pair of balanced transmissionlines, a shield electrode that opposes at least one of the balancedtransmission lines and the unbalanced transmission line, a pair ofbias-capacitor patterns, and a plurality of dielectric layers arestacked, a common bias terminal that is provided on a surface of thestack and that is electrically connected to the balanced transmissionlines and one capacitor pattern of the bias-capacitor patterns; and ashield terminal that is provided on a surface of the stack and that iselectrically connected to the shield electrode and the other capacitorpattern.

One of the unique features of this laminated balun transformer is thatthe common bias terminal and the shield terminal are electricallyindependent of each other.

With the unique arrangements described above, when a bias electrode isapplied to the common bias terminal, the bias electrode is applied toonly the balanced transmission lines via the bias capacitor, thusallowing for stable amplification of a balanced signal.

Other features, elements, characteristics and advantages of the presentinvention will become more apparent from the following detaileddescription of preferred embodiments thereof with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a laminated balun transformeraccording to a first preferred embodiment of the present invention.

FIG. 2 is a perspective view showing the outer appearance of the baluntransformer shown in FIG. 1.

FIG. 3 is an electrical equivalent circuit diagram of the baluntransformer shown in FIG. 2.

FIG. 4 is an electrical circuit diagram for illustrating effects of thebalun transformer shown in FIG. 2.

FIG. 5 is an exploded perspective view of a laminated balun transformeraccording to a second preferred embodiment of the present invention.

FIG. 6 is an electrical equivalent circuit diagram of the baluntransformer shown in FIG. 5.

FIG. 7 is an exploded perspective view showing a conventional laminatedbalun transformer.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A laminated balun transformer of the present invention will be describedbelow in conjunction with preferred embodiments thereof.

In each preferred embodiment, similar elements and similar portions aredenoted with the same reference numerals in the drawings.

First Preferred Embodiment, FIGS. 1 to 4

As shown in FIG. 1, a laminated balun transformer 21 includes dielectricsheets 22 a to 22 j. on the surfaces of the dielectric sheets 22 b, 22e, and 22 i, lead electrodes 23, 26, and 29 are provided, respectively.On the surfaces of the dielectric sheets 22 c, 22 d, 22 g, and 22 h,line elements 24, 25, 27, and 28, each having an electrical lengthcorresponding to a ¼ wavelength, are provided, respectively. On thesurfaces of the dielectric sheets 22 a, 22 f, and 22 j, shieldelectrodes 30, 31, and 32 are provided, respectively.

As a material for the dielectric sheets 22 a to 22 j, a resin, such asepoxy, or a dielectric ceramic is preferably used. In the firstpreferred embodiment, dielectric ceramic powder is preferably used as amaterial for the dielectric sheets 22 a to 22 j, and is mixed andkneaded with a binder or other suitable material. The resulting mixtureis then formed into ceramic green sheets. The thicknesses of thedielectric sheets 22 a to 22 j are set to predetermined values.

The lead electrode 23 has one end 23 a that is exposed at the middle ofthe proximal edge of the dielectric sheet 22 b, and the other end 23 bof the lead electrode 23 is located at the approximate center of thedielectric sheet 22 b. The line element 24 preferably has a spiralpattern configuration. One end 24 a of the line element 24 is exposed atthe middle of the distal edge of the sheet 22 c, and the other end 24 bthereof is located at the center of the dielectric sheet 22 c. The end24 b of the line element 24 is electrically connected to the end 23 b ofthe lead electrode 23 through a via hole 35 provided in the dielectricsheet 22 b.

The line element 25 preferably has a spiral pattern configuration. Oneend 25 a of the line element 25 is exposed at the left side of thedistal edge of the sheet 22 d, and the other end 25 b thereof is locatedat the approximate center of the dielectric sheet 22 d. One end 26 a ofthe lead electrode 26 is exposed at the left side of the proximal edgeof the sheet 22 e, and the other end 26 b thereof is located at theapproximate center of the dielectric sheet 22 e. The end 26 b of thelead electrode 26 is electrically connected to the end 25 b of the lineelement 25 through a via hole 35 provided in the sheet 22 d.

The line element 27 preferably has a spiral pattern configuration. Oneend 27 a of the line element 27 is exposed at the middle of the distaledge of the sheet 22 g, and the other end 27 b thereof is located at theapproximate center of the sheet 22 g.

The line element 28 has the shape of a spiral pattern. One end 28 a ofthe line element 28 is exposed at the right side of the distal edge ofthe sheet 22 h, and the other end 28 b thereof is located at theapproximate center of the dielectric sheet 22 h. One end 29 a of thelead electrode 29 is exposed at the left side of the proximal edge ofthe sheet 22 i, and the other end 29 b thereof is located at theapproximate center of the sheet 22 i. The end 29 b of the lead electrode29 is electrically connected to the end 28 b of the line element 28through a via hole 35 provided in the sheet 22 h.

The shield electrodes 30, 31, and 32 are provided on substantially theentire surfaces of the sheets 22 a, 22 f, and 22 j, respectively. Leadportions 30 a, 31 a, and 32 a therefor are exposed at the right side ofthe proximal edge of the dielectric sheets 22 a, 22 f, and 22 j,respectively. When the characteristics of the balun transformer 21 aretaken into account, the shield electrodes 30, 31, and 32 are preferablyarranged to be separated by a predetermined distance from the lineelements 24, 25, 27 and 28. The lead electrodes 23, 26, and 29, the lineelements 24, 25, 27, and 28, and the shield electrodes 30, 31, and 32are formed by sputtering, deposition, printing, or other suitableprocess, and include a material, such as Ag—Pd, Ag, Pd, or Cu, or othersuitable material.

The dielectric sheets 22 a to 22 j are stacked and integrally fired toprovide a stack 40, as shown in FIG. 2. A ground terminal G1, anunbalanced signal terminal 41, and a shield terminal G2 are formed onthe proximal side surface of the stack 40. Balanced signal terminals 42a and 42 b and a relay terminal 43 are formed on the distal side surfaceof the stack 40. The terminals 41 to 43, G1, and G2 are formed bysputtering, deposition, coating, or other suitable process, and includea material, such as Ag—Pd, Ag, Pd, Cu, or a Cu alloy, or other suitablematerial.

The unbalanced signal terminal 41 is electrically connected to the end23 a of the lead electrode 23, the balanced terminal 42 a iselectrically connected to the end 25 a of the line element 25, thebalanced signal terminal 42 b is electrically connected to the end 28 aof the line element 28, and the relay terminal 43 is electricallyconnected to the ends 24 a and 27 a of the line elements 24 and 27. Theground terminal G1 is electrically connected to the ends 26 a and 29 aof the lead electrodes 26 and 29, and the shield terminal G2 iselectrically connected to the lead portions 30 a to 32 a of the shieldelectrodes 30 to 32. FIG. 3 is an electrical equivalent circuit diagramof the laminated balun transformer 21.

In the balun transformer 21 having the above-described configuration,the line elements 24 and 25 are arranged between the shield electrodes30 and 31, and have a strip line structure. The line elements 27 and 28are also arranged between the shield electrodes 31 and 32, and have astrip line structure. The line elements 24 and 27 are connected inseries through the relay terminal 43, to constitute an unbalancedtransmission line 38, which is an impedance element. The line elements25 and 28 each constitute a balanced transmission line 39, which is animpedance element.

The line elements 24 and 25 are arranged so as to oppose each other withthe dielectric sheet 22 c interposed therebetween, and the line elements27 and 28 are arranged so as to oppose each other with the dielectricsheet 22 g interposed therebetween. Thus, the spiral pattern of the lineelement 24 and the spiral pattern of the line element substantiallyoverlap each other in plan view, and the opposing portions areelectromagnetically coupled (line coupling) to constitute a coupler.Similarly, the spiral pattern of the line element 27 and the spiralpattern of the line element 28 substantially overlap each other in planview, and the opposing portions are electromagnetically coupled (linecoupling) to constitute a coupler. While one end (specifically, the end27 a of the line element 27) of the unbalanced transmission line 38 isfree, it may be connected to ground.

For adjusting electrical characteristics of the balun transformer 21,the thicknesses of the dielectric sheets 22 c and 22 g and the linewidth of the line elements 24, 25, 27, and 28 are changed to adjust theelectromagnetic coupling between the line elements 24 and 25 or theelectromagnetic coupling between the line elements 27 and 28.

Since the ground terminal G1, which is electrically connected to thebalanced transmission lines 39, is electrically independent of theshield terminal G2, the ground terminal G1 can be used not only as aground terminal but also as a bias terminal or other terminal. Forexample, the balun transformer 21 may be incorporated into a portabletelephone or a mobile communication apparatus, or other suitableapparatus. In such a case, a balanced signal that propagates through thebalanced transmission lines 39 can be amplified by applying a biasvoltage to the ground terminal G1, which has conventionally beenconnected to ground.

FIG. 4 is an electrical circuit diagram showing a major portion of thebalun transformer 21 that is incorporated in a mobile communicationapparatus. The balun transformer 21 is connected between a filtercircuit Fil and a low-noise amplifier Amp. An unbalanced signal S1 thatis input from the filter circuit Fil is converted by the baluntransformer 21 into a balanced signal S2, which is then output from thebalanced signal terminals 42 a and 42 b to the low-noise amplifier Amp.

In this case, a bias voltage is applied to the ground terminal G1 of thebalun transformer 21. This causes the bias voltage to be applied to thelow-noise amplifier Amp, as a power-supply voltage for the low-noiseamplifier Amp, through the balanced transmission lines 39. As a result,the electrical circuit is simplified, which allows for miniaturizationof the mobile communication apparatus.

Additionally, the balun transformer 21 has a shielding effect since theshield electrode 30 is disposed on the upper surface thereof. Further,although the shield electrode 30 is exposed at the upper surfacethereof, the shield electrode 30 may be integrally covered by anotherdielectric sheet.

A case in which the balun transformer 21 is included as abalanced-to-unbalanced signal converter will now be described withreference to FIG. 3. When an unbalanced signal S1 is input to theunbalanced signal terminal 41, the unbalanced signal S1 propagatesthrough the unbalanced transmission line 38 (the lead electrode 23—lineelement 24—relay terminal 43—line element 27). Thus, the line element 24is electromagnetically coupled with the line element 25 and the lineelement 27 is electromagnetically coupled with the line element 28,thereby converting the unbalanced signal S1 into a balanced signal S2.The balanced signal S2 is then output from the balanced signal terminals42 a and 42 b. Conversely, when a balanced signal S2 is input to thebalanced signal terminals 42 a and 42 b, the balanced signal S2propagates through the balanced transmission lines 39, and is convertedby the unbalanced transmission line 38 into an unbalanced signal S1,which is then output from the unbalanced signal terminal 41.

Second Preferred Embodiment, FIGS. 5 to 6

A balun transformer according to a second preferred embodiment has aconfiguration in which a dielectric sheet 22 k, which has abias-capacitor pattern 33 on a surface thereof, is inserted between thedielectric sheets 22 a and 22 b of the balun transformer 21 of the firstpreferred embodiment. Thus, as shown in FIG. 5, the dielectric sheet 22k is provided between the dielectric sheets 22 a and 22 b, and thebias-capacitor pattern 33 is disposed at a surface of the dielectricsheet 22 k. A lead portion 33 a of the bias-capacitor pattern 33 isexposed at the left side of the proximal edge of the sheet 22 k. Thebias-capacitor pattern 33 and the shield capacitor-pattern 30 define abias capacitor C of, for example, about 30 pF. Thus, the shieldcapacitor-pattern 30 also defines a bias-capacitor pattern. The shapesof the capacitor patterns 30 and 33 are arbitrary, but it is preferablethat the capacitor pattern 30 is arranged to have a large area since itmust provide a shielding effect.

The dielectric sheets 22 a to 22 k are stacked and integrally fired toprovide a stack, as shown in FIG. 2. A common bias terminal G1, anunbalanced signal terminal 41, and a shield terminal G2 are disposed onthe proximal side surface of the stack. Balanced signal terminals 42 aand 42 b and a relay terminal 43 are disposed on the distal side surfaceof the stack.

FIG. 6 is an electrical equivalent circuit diagram of the laminatedbalun transformer 51. The common bias terminal G1 is connected to oneend of each of the balanced transmission lines 39 via the bias capacitorC. This arrangement can provide the laminated balun transformer 51 intowhich the bias capacitor C is incorporated.

The characteristics of the balun transformer 21 of the first preferredembodiment can deteriorate in some cases, when the ground terminal G1 isused as a bias terminal. The balun transformer of the second preferredembodiment, however, can prevent the characteristic deterioration, sinceit has the bias capacitor C between the common bias terminal G1 and theshield terminal (ground) G2.

Other Preferred Embodiments

The laminated balun transformer of the present invention is not limitedto the above-described preferred embodiments, and thus can be changedwithin the sprit and scope of the present invention.

For example, the line elements 24, 25, 27, 28 may have any shape, andthus may have a spiral, curved, or straight shape, or other suitableshape. In addition, the line elements do not necessary have to be set toa length of ¼ wavelength, and also the line widths of all the lineelements also do not have to be the same.

Additionally, the structure of the line elements is not limited to thestrip line structure arranged between two shield electrodes, and may bea so-called “microstrip line structure” in which line elements arearranged on the obverse surface of a dielectric substrate (on thereverse surface, a shield electrode is provided).

In the laminated balun transformers of various preferred embodimentsdescribed above, the coupler constituted by the line elements 24 and 25and the coupler constituted by the line elements 27 and 28 arevertically arranged in the stack in which the dielectric sheets 22 a to22 k are stacked. However, the couplers may be arranged side by side ona dielectric sheet.

Furthermore, the number of couplers constituted byelectromagnetically-coupled line elements is not limited to two, andthus may be three or more. For example, the balun transformer may be aso-called “dual balun transformer” having a pair of balancedtransmission lines and two unbalanced transmission lines that areelectromagnetically coupled with the balanced transmission lines.Alternatively, the balun transformer may include one unbalancedtransmission line and two pairs of balanced transmission lines that areelectromagnetically coupled with the unbalanced transmission line.

In addition, the electromagnetic coupling between the balancedtransmission line and the unbalanced transmission line is not limited toline coupling, and may also be coil coupling. Further, the descriptionin the various preferred embodiments has been given for a case in whicha bias voltage is applied to only the balanced transmission lines 39.When, however, one end (the end 27 a of the line element 27) of theunbalanced transmission line 38 is connected to ground, a groundterminal that is electrically connected to the unbalanced transmissionline 38 may be additionally provided such that a bias voltage is appliedto the ground terminal.

While preferred embodiments have been described in the case of a singleproduct by way of example, in the case of mass production, a motherboardhaving a plurality of balun transformers can be fabricated and cut intoproducts having a predetermined size. Further, in preferred embodimentsdescribed above, after the dielectric sheets on which conductors havebeen formed are stacked, the dielectric sheets are integrally fired.However, the present invention is not necessarily limited thereto. Thus,sheets that have been fired in advance may be used. In addition, thebalun transformer may be fabricated by the following method. Adielectric layer is preferably formed by applying a dielectric materialin paste form by printing or other suitable method, and a conductivematerial in paste form is applied to a surface of the dielectric layerto form a conductor. Next, a dielectric material in paste form isapplied onto the conductor. Overlaying pastes sequentially in thatmanner can provide a balun transformer having a stacked structure.

As described above, according to preferred embodiments of the presentinvention, since the ground terminal that is electrically independent ofthe shield terminal is provided, the ground terminal can also be usedas, for example, a bias terminal. Thus, applying a bias voltage to onlythe ground terminal that is connected to the balanced transmission linesallows for the amplification of a balanced signal propagating throughthe balanced transmission lines. In addition, incorporating the biascapacitor into the balun transformer allows a bias voltage to be appliedvia the bias capacitor, thereby achieving stable amplification of thebalanced signal.

As described above, the laminated balun transformer of preferredembodiments of the present invention can be advantageously used as abalanced-to-unbalanced signal converter, phase shifter, or other devicefor an IC for a wireless communication apparatus

While preferred embodiments of the invention have been described above,it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the invention. The scope of the invention, therefore, is to bedetermined solely by the following claims.

What is claimed is:
 1. A laminated balun transformer comprising: a stack in which, at least a pair of balanced transmission lines, an unbalanced transmission line that is electromagnetically coupled with the pair of balanced transmission lines, a shield electrode that opposes at least one of the balanced transmission lines and the unbalanced transmission line, and a plurality of dielectric layers are stacked; a ground terminal that is provided on a surface of the stack and that is electrically connected to the balanced transmission lines; and a shield terminal that is provided on a surface of the stack and that is electrically connected to the shield electrode; wherein the ground terminal and the shield terminal are electrically independent of each other.
 2. The laminated balun transformer according to claim 1, wherein the stack includes a plurality of dielectric sheets having lead electrodes and line elements disposed thereon.
 3. The laminated balun transformer according to claim 2, wherein each of the line elements has an electrical length corresponding to a ¼ wavelength.
 4. The laminated balun transformer according to claim 2, wherein shield electrodes are provided on the plurality of dielectric sheets.
 5. The laminated balun transformer according to claim 2, wherein the lead electrodes have a spiral configuration.
 6. The laminated balun transformer according to claim 2, wherein each of the lead electrodes are electrically connected to another of the lead electrodes through via holes formed in the stack.
 7. A laminated balun transformer comprising: a pair of balanced transmission lines; an unbalanced transmission line that is electromagnetically coupled with the pair of balanced transmission lines; an unbalanced signal terminal that is electrically connected to one end of the unbalanced transmission line; two balanced signal terminals, each of the two balanced signal terminals being electrically connected to one end of a corresponding one of the pair of balanced transmission lines; a common bias terminal that is electrically connected to the other ends of the pair of balanced transmission lines; and a bias capacitor that is electrically connected between the common bias terminal and ground.
 8. The laminated balun transformer according to claim 7, further comprising a stack including the pair of balanced transmission lines, the unbalanced transmission line, and a shield electrode that opposes at least one of the pair of balanced transmission lines and the unbalanced transmission line.
 9. The laminated balun transformer according to claim 8, wherein the stack includes a plurality of dielectric sheets having lead electrodes and line elements disposed thereon.
 10. The laminated balun transformer according to claim 9, wherein each of the line elements has an electrical length corresponding to a ¼ wavelength.
 11. The laminated balun transformer according to claim 10, wherein shield electrodes are provided on the plurality of dielectric sheets.
 12. The laminated balun transformer according to claim 10, wherein the lead electrodes have a spiral configuration.
 13. The laminated balun transformer according to claim 10, wherein each of the lead electrodes are electrically connected to another of the lead electrodes through via holes formed in the stack.
 14. The laminated balun transformer according to claim 8, wherein the common bias terminal and the shield electrode are electrically independent of each other.
 15. The laminated balun transformer according to claim 8, further comprising a ground terminal that is provided on a surface of the stack and electrically connected to the pair of balanced transmission lines, wherein the ground terminal and the shield terminal are electrically independent of each other.
 16. A laminated balun transformer comprising: a stack in which, at least a pair of balanced transmission lines, an unbalanced transmission line that is electromagnetically coupled with the pair of balanced transmission lines, a shield electrode that opposes at least one of the pair of balanced transmission lines and the unbalanced transmission line, a pair of bias-capacitor patterns, and a plurality of dielectric layers are stacked; a common bias terminal that is provided on a surface of the stack and that is electrically connected to the balanced transmission lines and one of the pair of bias-capacitor patterns; and a shield terminal that is provided on a surface of the stack and that is electrically connected to the shield electrode and the other of the pair of bias-capacitor patterns; wherein the common bias terminal and the shield terminal are electrically independent of each other.
 17. The laminated balun transformer according to claim 16, wherein the stack includes a plurality of dielectric sheets having lead electrodes and line elements disposed thereon.
 18. The laminated balun transformer according to claim 17, wherein each of the line elements has an electrical length corresponding to a ¼ wavelength.
 19. The laminated balun transformer according to claim 17, wherein shield electrodes are provided on the plurality of dielectric sheets.
 20. The laminated balun transformer according to claim 17, wherein the lead electrodes have a spiral configuration.
 21. The laminated balun transformer according to claim 17, wherein each of the lead electrodes are electrically connected to another of the lead electrodes through via holes formed in the stack. 